The present invention relates to a device for positioning of nozzles of a stator stage and for cooling of rotor discs in gas turbines.
As is known, gas turbines are machines which consist of a compressor and of a turbine with one or more stages, wherein these components are connected to one another by a rotary shaft, and wherein a combustion chamber is provided between the compressor and the turbine.
In order to pressurise the compressor, it is supplied with air obtained from the outer environment.
There is admission into the combustion chamber of the fuel, which is ignited by means of corresponding spark plugs, in order to produce the combustion, which is designed to give rise to an increase in the temperature and pressure, and thus to enthalpy of the gas.
Subsequently, via corresponding ducts, the high-temperature, high-pressure gas reaches the various stages of the turbine, which transforms the enthalpy of the gas into mechanical energy which is available to a user.
In two-stage turbines, the gas is processed in the first stage of the turbine, in temperature and pressure conditions which are quite high, and undergoes initial expansion there; whereas in the second stage of the turbine it undergoes second expansion, in temperature and pressure conditions which are lower than in the previous cases.
It is also known that in order to obtain the best performance from a specific gas turbine, the temperature of the gas needs to be as high as possible; however, the maximum temperature values which can be obtained in use of the turbine are limited by the resistance of the materials used.
In order to make apparent the technical problems solved by the present invention, a brief description is provided hereinafter of the system of stator nozzles and rotor blades of the various stages of a gas turbine according to the known art.
The first stage nozzle is used to supply the flow of burnt gases in suitable conditions to the intake of the first stage rotor, and, in particular, to guide it in an appropriate manner into the apertures of the rotor blades; thus preventing the flow from meeting directly the dorsal or convex surface and the ventral or concave surface of the blades.
The series of nozzles for the second stage of a gas turbine consists of an annular body, which in turn can be divided into nozzle segments, each segment generally consisting of nozzles which are defined or formed by three foils, which have a corresponding wing-shaped profile.
This series of nozzles for the second stage is in the shape of a ring, and is connected on the exterior to the turbine housing, and on the interior to a corresponding annular support.
In this respect, it should be noted that a first technical problem of the stators consists of the fact that the stator is subjected to high pressure loads, which are caused by the reduction of pressure between the intake and output of the nozzle.
In addition, the stators are subjected to high temperature levels, caused by the flow of hot gases obtained from the combustion chamber and from the preceding stage, as well as by the flows of cold air which are introduced inside the turbine, in order to cool the parts which are subjected to the greatest stress from the thermal and mechanical points of view.
A second problem which is particularly common according to the known art is that of guaranteeing optimum support and locking of the segments of the second stage nozzle, which counterbalances the forces which tend to displace and rotate the nozzle.
In addition, the conventional stators have support and locking systems which do not permit easy dismantling, if this is necessary in order to carry out operations of maintenance or replacement of one or more worn or damaged stator foils.
Another problem consists of the fact that the stators are subject to the vibrations transmitted by the stator vanes during functioning of the machine.
The object of the present invention is thus to provide a device for positioning of nozzles of a stator stage, and for cooling of rotor discs in gas turbines, which is particularly reliable, in order to eliminate the aforementioned problems in an optimum manner.
Another object of the invention is to provide a device for positioning of nozzles of a stator stage, and for cooling of rotor discs in gas turbines, which has a simple and compact structure.
Another object of the invention is to provide a device which has a low cost, and consists of a reduced number of component parts.
Yet another object of the invention is to provide a device for positioning of nozzles of a stator stage in gas turbines which permits easy fitting and dismantling of the stator vanes, as required, in order to maintain and optionally to replace the latter.
A further object of the invention is to provide a device which permits optimum resistance to the vibrations which affect the low-pressure stator vanes, thus preventing these vibrations from being transferred to the other elements of the motor.
A further object of the invention is to provide a device which makes it possible to compensate for the thermal expansion to which the segments of the nozzle are subject.
Another object of the invention is to provide a device which is safe, simple and economical.
This and other objects are achieved by a device for positioning of nozzles of a stator stage and for cooling of rotor discs in gas turbines, which is applicable to nozzle segments consisting of several foils, wherein each of the said nozzle segments is connected at the top to an outer ring to contain cooling air, and is positioned at the base on an inner ring, which makes it possible to arrange the said nozzle segments circumferentially relative to the axis of the said gas turbine, characterised in that, for each foil of the said nozzle segment, there is provided at least one tube, which is inserted in a corresponding duct present inside the said foils, which puts an area where the said cooling air circulates into communication with the high pressure disc and the low pressure disc.
According to a preferred embodiment of the present invention, the outer ring to contain the cooling air is associated with a mobile ring, which makes it possible to compensate for the differential thermal expansion which arises between the turbine housing and the outer ring.
According to another preferred embodiment of the present invention, the inner ring has receptacles for pins, wherein these pins are used for positioning of the nozzle segments.
According to a further preferred embodiment of the present invention, corresponding sealing rings are provided between the pins and the lower end of the foils of the nozzle segment.
In addition, the right- and left-hand pins are mounted such as to have radial play which is greater than the play relating to the central pin.
According to another preferred embodiment of the present invention, the inner ring has ducts which communicate respectively with the tubes and with the first stage disc and the second stage disc.
In addition, the pins have holes in order to permit communication by the cooling air between the tubes and the ducts of the inner ring.
Finally, according to the present invention, extraction of the pins from the inner ring is prevented by means of use of corresponding segments, which are inserted in a circumferential groove in the inner ring, and are shaped such as to have projections, which are folded inside holes present on the lower part of the said pins.
Finally, the inner ring has on its interior a honeycomb which is interfaced with the sealing teeth on the rotor, belonging to the high pressure stage.
Further characteristics of the invention are defined in the claims attached to the present patent application.